Heretofore, highly aromatic oils have been preferably used for rubber compositions for tires and other areas as the softener for rubber compositions and the extender for synthetic rubbers from the standpoint of providing the high loss property (the high hysteresis loss property) and affinity with the rubber.
Recently, the use of process oils having a content of extracts with DMSO smaller than 3% by mass, which are obtained by treating highly aromatic oil produced from petroleum as the raw material and called Treated Distilled Aromatic Extracts (TDAE) or Mild Extracted Solvates (MES), is increasing (for example, refer to Patent Reference 1).
However, the rubber compositions using a substitute oil such as TDAE and MES described above have a problem in that the temperature dependency of the viscoelastic properties of the rubber composition tends to shift to the low temperature side in comparison with that exhibited by the use of a conventional highly aromatic oil due to the lower softening point and smaller viscosity of the oil itself to cause decreases in the glass transition temperature (Tg) and the storage modulus (E′), and the wet skid resistance and the steering stability of the tire are decreased.
However, the rubber compositions using a substitute oil such as TDAE and MES described above have a problem in that the temperature dependency of the viscoelastic properties of the rubber composition tends to shift to the low temperature side in comparison with that exhibited by the use of a conventional highly aromatic oil due to the lower softening point and smaller viscosity of the oil itself to cause decreases in the glass transition temperature (Tg) and the storage modulus (E′) with increase in the amount of the use, and the wet skid resistance and the steering stability of the tire are decreased.
When a conventional method for increasing the storage modulus, for example, increasing the amount of a reinforcing filler such as carbon black and silica or decreasing the amount of an oil, is conducted to overcome the decrease in the steering stability, viscosity of the unvulcanized rubber is increased, and workability in plants deteriorates markedly.    [Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 11(1999)-302459